The invention relates to a method for prioritizing information to be transmitted in cell streams.
In up-to-date ATM systems, information is transmitted in cells. These cells have a header part and an information part. The connection information is stored in the header part and the traffic data to be transmitted is stored in the information part. The actual transmission usually takes place via connection sections between the transmitter and the receiver. In the process, there may possibly be the need to utilize the connection sections in such a way that a plurality of transmission devices transmit the cell streams originating therefrom via the same connection section.
In order to be able to transmit the respective cell streams in accordance with the requirements of the individual cell streams, a so-called WEIGHTED FAIR QUEUING SCHEDULING method has become established as the state of the art. The corresponding conditions are indicated, for example, in the publication xe2x80x9cVirtual Spacing for Flexible Traffic Controlxe2x80x9d, J. W. Roberts, International Journal of Communication Systems, Vol. 7, 307-318 (1994). Here, the individual cell streams are allocated different weighting factors with which the actual transmission procedure to the individual connection sections is controlled. In order to understand this better, please refer to FIG. 3.
Here, cell streams 1 . . . n are disclosed by way of example. The n cell streams are directed by a transmission device DEMUX in the direction of one or more receivers. In practice, only one common connection section is used in this context. In addition, weighting factors r1 . . . rn are allocated to n cell streams. For the sake of easier comprehension, it will be assumed that only two cell streams, namely the cell streams 1, 2 are to be routed via one connection section. In addition, the connection section is to have a maximum transmission capacity of 150 Mbit/sec. The two cell streams 1 and 2 are allocated weighting factors r1=2 and r2=1. The effect of this is that cell stream 1 is transmitted at a transmission rate of 100 Mbit/sec and cell stream 2 is transmitted at only 50 Mbit/sec if cells are waiting to be transmitted.
The problem with such a procedure is that the capacity utilization of the connection is not ensured to an optimum degree, in particular in terms of different services. This is particularly due to the fact that, for example, connections with guaranteed service quality have to be treated differently from, for example, connections without any service quality guarantees. Thus, the former are, as a rule, switched through as a function of the service quality parameters and/or connection parameters, something which is less significant in the case of the latter. Here, the necessary data are transmitted only if the connection section is otherwise subjected to low loading. This is the case in particular if the cell streams do not fully utilize the available transmission capacities.
The invention is based on the object of indicating a way in which the capacity utilization of connection sections can be controlled in an optimum and efficient fashion when the WEIGHTED FAIR QUEUING SCHEDULING method is being used.
The invention is achieved on the basis of the features disclosed in the preamble of Patent claim 1, by means of the features of the characterizing part.
An advantage with the invention is, in particular, that prioritization is achieved by selection of extreme values of the weighting factors. This entails the advantage that the cell streams via the respective connection section can be controlled as a function of these priorities, and optimum capacity utilization is thus ensured.
Further refinements of the invention are given in the subclaims:
According to claim 2 there is provision for the cell streams to be formed from a plurality of substreams to which, if appropriate, different weighting factors are allocated in each case. This entails the advantage that the transmission of information within one connection section can be carried out with different priorities.
In accordance with claim 3 there is provision that, if appropriate, different weighting factors are allocated to the substreams of a cell stream. This entails the advantage of prioritizing information within a cell stream.
In accordance with claim 4 there is provision that at least one counting device is provided per substream and priority, the counter reading of which is incremented when a cell of the respective substream arrives and is decremented when a cell of the respective substream leaves. This entails the advantage that the occupancy level of cells in the system can be detected.
In accordance with claim 5 there is provision for a scheduler to pass on the cells according to the valuation of the counting devices.
This entails the advantage of a particularly efficient utilization of the connection section.
The invention is explained in more detail below with reference to an exemplary embodiment.